This invention is concerned generally with controlling the operation of a DC arc furnace and is more particularly concerned with controlling and limiting the incidence of arcing between furnace components.
The processes which give rise to unwanted arcing between furnace components in a DC arc furnace are not readily understood nor predictable. A voltage gradient should however be established between various components of the furnace in such a way that the voltage difference between any two components is below a threshold voltage at which arcing could occur.
The threshold voltage is dependent on a number of variable parameters. Also the voltage between any two components may also be affected by operating conditions. Consequently although a particular voltage difference between two components of a furnace may not, initially, be in excess of the relevant threshold voltage the operating conditions may change in such a way that the threshold voltage is in fact exceeded and arcing occurs.
The effect of unwanted arcing can be catastrophic. It is essential therefore to detect an arc as soon as possible after it occurs and to take action to extinguish the arc.
Although the incidence of arcing can be minimised by operating a furnace at rated power with a low voltage and high current it is difficult to justify this type of approach on economic grounds. On the contrary it is desirable to operate a furnace at its rated power output with a high voltage but under operating conditions such that arcing is unlikely to occur. If however unwanted arcing does take place action must be initiated as soon as possible to limit damage and thereafter to restore the furnace to an effective operating situation so that down-time is reduced.